The present invention relates, in general, to cold-cathode field emission devices, and more particularly, to a field emission device employing a novel current limiting protection scheme.
Field emission devices (FEDs) are well known in the art and are commonly employed for a broad range of applications including image display devices. Examples of such FEDs are described in U.S. Pat. No. 5,191,217 issued to Kane et al. on Mar. 2, 1993, and U.S. Pat. No. 5,142,184 issued to Robert C. Kane on Aug. 25, 1992. Prior FEDs typically have an emitter or emission tip that is utilized to emit electrons that are attracted to a distally disposed anode. A ballast resistor generally is connected in series with the tip to limit current flow through the tip in order to prevent damaging the tip. Because of the large resistor values needed for the ballast resistor, it is difficult to control both the resistivity and the temperature coefficient of semiconductor material in the high resistivity ranges, typically 1000 ohm-centimeter (ohm-cm.) or greater, required for the ballast resistors.
Another problem with these prior FEDs is the high voltage values that must be switched in order to enable and disable the FED. Electron emission typically is disabled by applying a high voltage, about 100 volts, to the emission tip and to the emission grid or gate, conversely, electron emission is enabled by applying a lower voltage, generally about zero volts, to the tip. Switching such large voltages results in high power dissipation in addition to long rise and fall times for the drive signal.
Accordingly, it is desirable to have an FED emission tip current limiting mechanism that does not require precisely controlled resistivity or resistor values, and that does not switch large voltages to enable and disable electron emission.